Good question re 7 and 8.
Current class is six T45s for RN plus an option for two additonal ships. The BAE business case is now based on six ships, although initial costings were for 12, which partially explains why each platform is now more expensive than initially thought (development costs spread over half the number, supplier costs scaled up accordingly etc).
There have been some rumours that Saudi Arabia might take the two options. Not sure how realistic that prospect is though. Guess that's a question for UKG.